The bearing caps are held stationary in the drive shaft yokes. Roller bearings fit between the caps and the cross to reduce friction. The cross is free to rotate inside the caps and yokes. Snap rings usually fit into grooves cut in the caps or the yoke bores to secure the bearing caps and bearings. There are several other methods of securing the bearing caps in the yokes. These are bearing covers, U-bolts, and bearing caps.

Figure 5-4.- Speed fluctuations caused by conventional universal joints.

Figure 5-5.- Cross and roller universal joint- disassembled view.

Ball and Trunnion Universal Joint
The ball and trunnion universal joint is a T-shaped shaft that is enclosed in the body of the joint (fig. 5-6). The trunnion ends are each equipped with a ball, mounted in needle bearings. and move freely in grooves in the outer body of the joint, in effect, creating a slip joint. Compensating springs at each end of the drive shaft hold it in a centered position.

Variations in length is permitted by the longitudinal movement of the balls in the body grooves. Angular displacement is allowed by outward movement of the balls on the trunnion pins. This type of universal joint is recognized easily by the flexible dust boot that covers it.

Double-Cardan Universal Joint
The double-cardan universal joint uses two cross and roller joints in tandem to form a single joint (fig. 5-7). The joints are linked through a centering yoke that works in conjunction with a specially designed spring-loaded centering ball. The components are contained within the centering coupling yoke.

As the shafts rotate, the action of the centering ball and yoke acts to maintain an equally divided drive angle between the connected shafts, resulting in a constant drive velocity.